feat: add MCP servers dashboard page with CRUD and token management

New page at /mcp-servers to register, view, and manage MCP server
instances. Shows endpoint config, enabled tools, and access tokens
with reveal/regenerate controls. Includes McpServerConfig model in
compliance-core, MongoDB collection accessor, server functions for
list/add/delete/regenerate-token, sidebar nav entry, and full CSS.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

compliance-dashboard/src/components/sidebar.rs

@@ -57,6 +57,11 @@ pub fn Sidebar() -> Element {
             route: Route::DastOverviewPage {},
             icon: rsx! { Icon { icon: BsBug, width: 18, height: 18 } },
         },
+        NavItem {
+            label: "MCP Servers",
+            route: Route::McpServersPage {},
+            icon: rsx! { Icon { icon: BsPlug, width: 18, height: 18 } },
+        },
         NavItem {
             label: "Settings",
             route: Route::SettingsPage {},